Electron image device



Sept. 16, 1.941.

G. A. MORTON ELECTRON IMAGE DEVICE Filed Aug. 51, 1959 "3F 1 M i: W a Flu Lw IL? 1 a .m i A F 4. a r: f A w 300 a mo l l l l ll Patented Sept. 16, 1941 OFFICE ELECTRON IMAGE DEVICE George A. Morton, Haddon Heights, N. J assignor to Radio Corporation of America, a corporation of Delaware ApplicationAugust 31, 1939, Serial No. 292,804-

'7 Claims.

This invention relates to electron optical systems of the type designed to handle extended or entire electron images (as distinguished from images built up or scanned by a moving pencil or beam of electrons) and constitutes an improvement upon the invention disclosed in copending application to Ramberg and Morton, Serial No. 199,110, filed March 31,1938, entitled Electron image devices.

'It is demonstrated in the ab'oveidentified disclosure that the electrons leaving any given object point in the usual electron image device are subject to various degrees of convergence in passing to the next succeeding electrode. As a result, some of the electrons are directed toward and impinge upon points other than the image points correction of the said image defects is achieved.

The electron mirror employed in the said device is inclined at angle with respect to both the electron source and the target electrode, hence the curvature introduced in the principal paths of the electrons may give rise to other, usually less obvious, image defects due to the large angle in the paths traversed by the electrons in passing from the source to the target electrodes and which may also be due to the use of a magnetic field for directing the electrons comprising the image in curved paths to and from the mirror;

Accordingly, the principal object of the invention is to retain the benefits of the correction of chromatic aberrations by means of the electron mirror without either employing a magnetic field to alter the directions of the electrons or causing them to enter the mirror fields at angles in excess of the normal field angles-of the electronoptical system.

Another object of the invention is to provide a simplified electron optical system for electron tubes of the type incorporating an electron mirjror and primary and secondary focusing elements, and wherein the mirror comprises two or more of the focusing elements.

Other objects and advantages of the invention will be apparent by reference to the following specification and to the accompanying drawing wherein Figure 1 is a longitudinal sectional View of an electron image tube incorporating an electron mirror and constructed in accordance with the principle of the invention,

Figure 2 is a longitudinal sectionalview of another embodiment of the invention showing the mirror elements incorporated in an oversize primary lens system, and

Figure 3 is a similar view of another embodiment of the invention.

In Fig. 1 T designates a highly evacuated envelope having a transparent window W adjacent which a photosensitive transparent image cathode C is mounted. A suitable optical lens system, not shown, may be provided, exterior of the tube for focusing a panchromatic or monochromatic light image upon the cathode. A series of spaced rings I, 2 and 3, in the first of which the cathode C is seated, and a short cylinder 4, constitute a primary electron lens system having an axis of symmetry cc, and which, when supplied with suitable potentials from a source exemplified in the drawing by a voltage divider R, serves to focus the photo or primary electrons from the cathode upon that (upper) part of a secondary electron emissive surface or multiplying electrode E which is mounted in line with said cathode adjacent the opposite end of the envelope.

Electrode E, or at least that part of it upon 7 which the primary electron image impinges is treated with caseium or equivalent substance to enhance its ability to release a multiplied family of secondary electrons upon impact of the primary electrons thereon. Like the cathode C, electrode E is preferably curved to correct for certain image defects. The center of the curvature of the electrode E lies on the axis of symmetry b-b of its lens system.

The rings 5, 6, 7, 8 and 9 and the short cylinder iii in front of the multiplying electrode E and through which the primary electrons fromthe cathode C pass constitute an electrostatic lens system for focusing the secondary or impact electrons from electrode E in the return direction to an electron mirror which, in the illustrated embodiment of the invention, comprises a pair of cylinders M M These cylinders are mounted on the cathode side of electrode E along an axis cc which is parallel to the axes ell-a, bb of the primary and secondary electron focusing elements and which is normal to the plane of the surfaces of the cathode C and multiplying electrode E.

It will be observed from an inspection of Fig. 1 that the surfaces of the lens cylinders M M fall substantially along the axis bb of the lens systems for the secondary electrons. If desired, these surfaces may be arranged to coincide exactly with the said axis bb. It follows, therefore, that the trajectories of the electrons entering the mirror lie within the normal field angles of the lens system (comprising elements to ID) for the multiplying or intensifying electrode E. The electrons constituting the intensified secondary-electron image from the multiplying electrode E and which enter the space circumscribed by the mirror cylinders M and M are reflected and accelerated in the return direction toward, and impinge upon, the output electrode S which is shown seated within a cylinder 1 l.

A shield A contiguous the inner Wall of the tube and surrounding the space intermediate the primary and secondary electron lens systems may be considered as forming no part of either these lens systems or the mirror, since it serves merely to prevent the accumulation of stray electrons upon the glass.

In operating the device of Fig. 1, the cathode may be adjusted to a potential of, say, 100 volts positive with respect to ground and with respect to the mirror cylinder M in which case the focusing cylinders 4 and H], the mirror element M the supporting cylinder II for the screen S, and the shield A are adjusted to a common potential of, say, 5000 volts positive with respect to M As indicated in the drawing, in this case, the intensifying or multiplying electrode E may be maintained at a potential of, say, 1000 volts positive with respect to the said most negative electrode and the focusing electrodes 2, 3, l, 8, and 9 at separate potentials each somewhat higher than the next preceding electrode in point of electron travel.

With the device thus energized, it will be ap parent that the primary electrons from the cathode C will enter the cylinder ID of the secondary electron lens at a velocity of 5000 volts. At such speed, the primary electrons will be substantially uninfiuenced by the focusing rings 9, 8, l, 6 and 5 of the secondary electron lens system. The secondary electrons released by the impact of the relatively high speed primary electrons upon the emissive portion of electrode E leave that electrode at very low velocities and are thus susceptible to the focusing action of the electrostatic field between the lens elements 5 to I 0, inclusive.

Since it is the property of the described type of electrostatic lens system to form an inverted electron image, all of the electrons released from the emissive area on the cathode C will enter lens cylinders |05 and impinge the intensifying electrode E in the form of an inverted image. Similarly, the intensified image from electrode E will enter the mirror cylinders M and M in the form of a reinverted image which will be focused upon the screen S in the form of an intensified reflected image corresponding to the light image impressed upon the cathode C.

In accordance with the invention, the electron mirror may be incorporated in and may form part of the lens system through which the primary electrons pass in their journey to the intensifying electrode. Thus, referring to Fig. 2, the mirror elements M and M may be mounted in line with the rings or cylinders ill-24 so that, with the same relative potential distribution described in connection with the device of Fig. 1, they form part of the lens system for focusing the electrons from the oathode 20 upon the intensifying electrode 2E. Where, as in this embodiment of the invention, the focusing rings 2|-24 are of the same diameter as the mirror elements, the light image impressed upon the cathode ZC by the optical lens L should be confined to that area of the cathode surface which will cause the primary electrons to enter the lens elements 30-41 and impinge upon the multiplying electrode 2E. As in the embodiment of the invention described in connection with Fig. 1, the secondary electrons comprising the intensified electron image from electrode E are reflected by the mirror elements M into the cylinder 3| and appear upon the fluorescent screen S in the form of an intensified optical image.

Where the electrons comprising the primary image are caused to pass through the mirror elements in their journey to the target electrode, it is not necessary that the primary lens elements be of the same oversize diameter as the mirror elements, as they are in the device of Fig. 2. Thus, referring to Fig. 3, the diameter of the lens elements GI, 42, 43, 44 through which the primary electrons from the cathode 3C pass before entering the mirror elements M M may be of the same diameter as the lens elements 41, 4B, 45, 44, which focus the secondary e1ectrons from the intensifying electrode 3E into the mirror, i. e., they may be of substantially the same diameter as the optical image which the device is designed to handle. As in the earlier described embodiments of the invention, the output electrode is here exemplified by a fluorescent screen 35 supported Within a supporting cylinder 48. In this embodiment of the invention the shield (A, Figs. 1 and 2) surrounding the space between the primary and secondary electron lens systems may be dispensed with, since the mirror elements themselves serve to prevent the accumulation of a positive charge upon the walls of the glass envelope. In operating this device the same relative potential distribution may be employed as is described in connection with the device of Fig. 1.

Various modifications of the invention will suggest themselves to those skilled in the art. It is to be understood, therefore, that the foregoing description of certain preferred embodiments of the invention is to be interpreted as illustrative and not in a limiting sense except as required by the prior art and by the spirit of the appended claims.

What is claimed is:

1. An electron discharge device comprising an image cathode, a multiplying electrode adapted to release an intensified electron image in response to the impress thereon of an electron image from said image cathode, an electron mirror comprising a plurality of apertured electrodes located on the cathode side of said multiplying electrode in spaced relation thereto and adapted to reflect said intensified electron image in the return direction, and an image target facing the mirror and upon which said reflected intensified electron image impinges.

2. The invention as set forth in claim 1 and wherein said electron mirror is mounted along an axis which is substantially normal to the surface of said image cathode.

3. The invention as set forth in claim 1 and wherein said electron mirror is mounted along an axis which is substantially normal to the surface of said multiplying electrode.

4. The invention as set forth in claim 1 and wherein said electron mirror is mounted along an axis which is substantially normal to the surface of said target electrode.

5. The invention as set forth in claim 7 and wherein said electron mirror comprises a plurality of apertured electrodes mounted along an axis which is substantially parallel to the axis of the electrodes which focus said primary electron image upon said multiplying electrode.

6. The invention as set forth in claim 7 and wherein said electron mirror comprises a plurality of apertured electrodes mounted along an axis which is substantially parallel to the axis of the electrodes which focus said multiplied electron image upon said mirror.

'7. An electron discharge device comprising an image cathode, a secondary electron emissive image intensifying electrode and an image 'target electrode located on the emissive side of said image cathode in spaced relation thereto and offset one from the other, a plurality of apertured electrodes through which a primary electron image from said cathode passes to said intensifying electrode, and an electron mirror located on that side of said intensifying and target electrodes which faces said cathode for reflecting the intensified image from said secondary emissive electrode upon said target electrode, said electron mirror comprising at least some of the apertured electrodes through which said primary electron image passes.

GEORGE A. MORTON. 

